With the continuing trend toward compact electronic apparatus, there is an ever-increasing demand for miniaturized interconnection systems between the electronic components of the apparatus. An example is in computer apparatus wherein there is a constant demand to reduce the thickness or height parameters of the electronic components. With the components mounted on a printed circuit board, the height parameters relate to the distance above the board in which desired interconnections are made and which constantly are being reduced. One type of electrical connector used in such applications is a right-angled connector which has a mating axis generally parallel to the printed circuit board, and with a plurality of terminals having right-angled tail portions projecting from the connector generally parallel to the board and then downwardly perpendicular to the board for interconnection with circuit traces on the board.
An example of the use of such electrical connectors is to interconnect signal transmission lines to printed circuit boards, other electronic devices or to other complementary connectors. The transmission lines transmit signals through a plurality of conductors which, preferably, are physically separated and electromagnetically isolated along their length. In the electronics industry, particularly the computer industry, the predominant system embodies a plurality of plug-in type connectors in mating engagement with receptacle connectors on the computer, its main printed circuit board or other electronic devices. One of the connectors often is a right-angled connector, as described above. The transmission lines typically include coaxial electrical cables, either in round or flat form, and round cables presently are being used predominantly in relatively high frequency applications between various system components.
Classical coaxial designs derive their characteristic impedance from the geometrical relationship between the inner signal conductors and an outer shield member and an intervening dielectric constant. For a given impedance, signal conductor size and dielectric material, an overall outside dimension is defined. The circuit characteristics along equal lengths of such conductors should be identical. In order to increase signal density and reduce the overall outside dimensions of a transmission line connector system, alternate geometries and/or dielectric systems are required.
When using a right-angled electrical connector in systems described above, problems are encountered because of the unequal lengths of the tail portions of the connector terminals and, therefore, the unequal circuit path lengths through the terminals. For instance, a typical right-angled connector has two rows of terminals running generally parallel to a printed circuit board, with tail portions of the terminals projecting from the connector housing and then downwardly for interconnection with circuit traces on the board. Obviously, the tail portions of the upper row of terminals are longer than the tail portions of the lower row of terminals. Consequently, in any given pair of terminals taken from both the upper and lower rows, unequal circuit path lengths are created through those terminals. The different path lengths result in different circuit characteristics. In particular, assuming that the regional dielectric constant is the same for both terminals and the connector exhibits a varying and non-homogenous impedance characteristic through its mated electrical path length, the terminal with the longer tail portion will create a different impedance characteristic in its circuit than the terminal with the shorter tail portion.
Although this is the general case, typically, when impedance correction is desired, it would be most commonly used to decrease the impedance of the longer tail portion. This is the more common case since most contact mating regions are more substantial in relative conductive plate areas than are the corresponding tail section, therefore exhibiting greater capacitive coupling and a reduced characteristic impedance. In this situation, one would typically seek to reduce the impedance of the longest tail section to bring it closer to the lower composite impedance provided by the contact mating region and shorter tail portion.
In the alternative, given a mating area with reduced capacitive coupling, one could reduce the impedance of the shorter tail section to bring it closer to a lower composite impedance yielded by a higher impedance contact mating region weighted by a lower impedance along the length of a longer tail portion. The terminal with the longer tail portion also will have a higher propagation delay than the terminal with the shorter tail portion (i.e. the propagation rate through the shorter tail portion is faster).
This invention is directed to solving the problems outlined above by provided a system in which such circuit characteristics as impedance and propagation delay can be altered in a very simple manner, particularly in a right-angled electrical connector.